In the past decade the density per unit area of electronic devices, such as very large scale integrated (VLSI) circuits, has greatly increased. By some estimates this increase in density has been on the order of 10,000 times what it was earlier. The space or area available with a VLSI circuit in which to make the large number of necessary connections to and from it and other circuitry is becoming almost vanishingly small measured by previous standards. As a result, there is now a difficult problem in providing easily mateable connections to and from the VLSI circuits when they are being tested, which connections are also small enough to fit the minute spaces available, and which are reliable and easily manufacturable.
In the present inventor Walsh's U.S. Pat. No. 4,554,506, which has an assignee in common with the present patent application, there is disclosed a modular probe assembly for use in testing VLSI circuits. This probe assembly utilizes a large number of relatively very long thin wire contact "beams" mounted in holes on close centers around the sides of plastic guide elements. These guide elements are stacked together vertically into an assembly. The holes in the guide elements are intentionally not aligned vertically in order to "bow" or pre-buckle each of the contact beams. This pre-buckling helps control the force of each contact beam when its end contacts and wipes against a surface pad on a VLSI circuit. The contact beams are permitted to flex dynamically near their lengthwise mid-points when the beams are pressed into contact with the surface pads of the VLSI circuit. In actual practice, because of the relatively large degree of dynamic flexing of the contact beams and in order to insure that they do not touch each other and cause electrical short-circuits, the beams were made of thin, pre-insulated wires. By way of example, the wires were about 4 mils in diameter with about one mil of insulation (such as polyimide). It has been found however that occasionally some of the insulation on the wires in the vicinity of their ends rubs off and comes between the ends and the contact pads on a VSLI circuit under test. This causes erratic electrical results and necessitated careful and regular cleaning of the contact beams.
As VLSI circuits have become even more dense, it has become desirable to provide contact "beams" or elements of a probe assembly throughout an area rather than merely around the periphery of the test probe assembly. But this in turn leads to the problem of making individual electrical connections from other circuitry (e.g., test equipment) to each of the densely packed contact elements of the probe assembly. By way of example, there may be a density of 10,000 or more surface pads per square inch of area of a VLSI circuit with the corresponding need to space the contact elements of a probe assembly on 10 mil or closer centers in both the "X" and "Y" directions. It is desirable to provide an effective and economical solution to this need.